R A N G E A N D I N T E N S I T Y C A LC U L AT I O N S
Nominal Range
The nominal range or effective intensity of a lantern comes from the following calculation known as Allard’s Law documented in
IALA Recommendations E-122 (2001) and E-200-2 (2008):
Ie =
E × D2
0.05
Ie
E
D
V
D
V
=
=
=
=
effective intensity (cd)
threshold of detection (lux)
nominal range (m)
visibility (m)
Threshold of detection is 0.0000002 lux for a lantern at night-time with no background light.
Visibility is a function of atmospheric transmissivity. Typically, transmissivity (T) = 0.74 and V = 18520 m (10 NM). At equatorial
latitudes and clear skies, T = 0.85 and V = 34262 m (18.5 NM).
Effective Intensity
The effective intensity of a flashing lantern comes from the following calculation known as Schmidt-Clausen or Blondel-Rey
documented in IALA Recommendations E-122 (2001) and E-200-4 (2008). This method is valid for the rectangular, non-fluctuating
flash profiles below the flicker fusion frequency (60 Hz) used by Carmanah lanterns.
Ie =
Ip × F
C+F
Ie
Ip
C
F
=
=
=
=
effective intensity (cd)
peak intensity (cd)
visual time constant (s)
flash duration (s)
The visual time constant is 0.2 s for a lantern at night-time.
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R A N G E A N D I N T E N S I T Y C A LC U L AT I O N S
NIGHT TIME RANGE AND INTENSITIES
RANGE
(NM)
eFFECTIVE INTENSITY (cd)
t = 0.74
T = 0.85
RANGE
(NM)
eFFECTIVE INTENSITY (cd)
t = 0.74
T = 0.85
0.5
0.2
0.2
3.8
31
18
0.6
0.3
0.3
3.9
34
20
0.7
0.4
0.4
4.0
37
21
0.8
0.6
0.5
4.1
40
22
0.9
0.7
0.6
4.2
43
24
1.0
0.9
0.8
4.3
46
26
1.1
1.2
1.0
4.4
50
27
1.2
1.4
1.2
4.5
54
29
1.3
1.7
1.4
4.6
58
31
1.4
2.0
1.7
4.7
62
33
1.5
2.4
2.0
4.8
67
34
1.6
2.8
2.3
4.9
72
37
1.7
3.3
2.6
5.0
77
39
1.8
3.8
3.0
5.1
83
41
1.9
4.4
3.4
5.2
89
43
2.0
5.0
3.8
5.3
95
46
2.1
5.7
4.3
5.4
102
48
2.2
6.4
4.7
5.5
109
51
2.3
7.3
5.3
5.6
116
53
2.4
8.1
5.8
5.7
124
56
2.5
9.1
6.4
5.8
132
59
2.6
10
7.1
5.9
141
62
2.7
11
7.8
6.0
150
65
2.8
12
8.5
6.1
160
69
2.9
14
9.2
6.2
171
72
3.0
15
10
6.3
181
76
3.1
17
11
6.4
193
80
3.2
18
12
6.5
205
83
3.3
20
13
6.6
218
87
3.4
22
14
6.7
232
91
3.5
24
15
6.8
246
96
3.6
26
16
6.9
261
100
3.7
29
17
7.0
277
105
Document: RangeIntensityCalculations_RevA
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